This invention relates to a traffic signal which makes use of transparent semiconductor elements in its light-emitting display section.
Conventional traffic signals make use of lamps of an ordinary type having a filament as the source of light. To display green for "safe", red for "danger" and yellow for "warning", transparent colored members such as tinted glass pieces are placed in front of individual lamps which are turned on one at a time. In other words, a conventional traffic signal contains two or three independent lamps disposed next to each other as shown in FIG. 6.
With a conventional traffic signal, filaments of its lamps cannot be prevented from breaking suddenly. For this reason, signal lamps are replaced regularly by new ones at a fixed interval, such as once a year. The cost and labor involved in this process are enormous. Another disadvantage of these conventional traffic signals is that the colored glass surfaces reflect light when a strong beam of light is directly incident thereon. When this happens, it is often impossible to tell which of the signal lamps is lit and this may cause a serious traffic accident. Still another disadvantage of these filament lamps is that their energy efficiency is low and hence that their rate of power consumption is high. Moreover, the light-emitting surface of a filament lamp is very small compared to the area of display such that it is nearly a point light source. Although a beam expander is used to expand the beam uniformly, it is difficult to achieve a completely uniform distribution in brightness.
Japanese Patent Publication No. 59-194286, for example, has disclosed a traffic signal making use of an arrangement of a large number of light-emitting diodes adapted to emit light of different colors, to display green, red, and yellow. Even with light-emitting diodes, however, three display sections corresponding to three different colors are necessary and the signal cannot be made smaller. Besides, it is both cumbersome and time-consuming to arrange thousands of light-emitting diodes in a plane.